Ligand-dependent interaction of the glucocorticoid receptor with p53 enhances their degradation by Hdm2.
Journal: 2001/October - Genes and Development
ISSN: 0890-9369
Abstract:
The glucocorticoid receptor (GR) and the tumor suppressor p53 mediate different stress responses. We have studied the mechanism of their mutual inhibition in normal endothelial cells (HUVEC) in response to hypoxia, a physiological stress, and mitomycin C, which damages DNA. Dexamethasone (Dex) stimulates the degradation of endogenous GR and p53 by the proteasome pathway in HUVEC under hypoxia and mitomycin C treatments, and also in hepatoma cells (HepG2) under normoxia. Dex inhibits the functions of p53 (apoptosis, Bax, and p21(WAF1/CIP1) expression) and GR (PEPCK and G-6-Pase expression). Endogenous p53 and GR form a ligand-dependent trimeric complex with Hdm2 in the cytoplasm. Disruption of the p53-HDM2 interaction prevents Dex-induced ubiquitylation of GR and p53. The ubiquitylation of GR requires p53, the interaction of p53 with Hdm2, and E3 ligase activity of Hdm2. These results provide a mechanistic basis for GR and p53 acting as opposing forces in the decision between cell death and survival.
Relations:
Content
Citations
(37)
References
(78)
Drugs
(3)
Chemicals
(7)
Genes
(3)
Organisms
(1)
Processes
(1)
Anatomy
(3)
Similar articles
Articles by the same authors
Discussion board
Genes Dev 15(18): 2367-2380

Ligand-dependent interaction of the glucocorticoid receptor with p53 enhances their degradation by Hdm2

Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, BP 163, 67404 Illkirch cedex, France
Present address: Laboratory of Human Carcinogenesis, Building 37, Room 2C23, 37 Convent Drive, National Cancer Institute, NIH Bethesda, MD 20892, USA.
Corresponding author.
Received 2001 Mar 5; Accepted 2001 Jul 26.

Abstract

The glucocorticoid receptor (GR) and the tumor supressor p53 mediate different stress responses. We have studied the mechanism of their mutual inhibition in normal endothelial cells (HUVEC) in response to hypoxia, a physiological stress, and mitomycin C, which damages DNA. Dexamethasone (Dex) stimulates the degradation of endogenous GR and p53 by the proteasome pathway in HUVEC under hypoxia and mitomycin C treatments, and also in hepatoma cells (HepG2) under normoxia. Dex inhibits the functions of p53 (apoptosis, Bax, and p21 expression) and GR (PEPCK and G-6-Pase expression). Endogenous p53 and GR form a ligand-dependent trimeric complex with Hdm2 in the cytoplasm. Disruption of the p53–HDM2 interaction prevents Dex-induced ubiquitylation of GR and p53. The ubiquitylation of GR requires p53, the interaction of p53 with Hdm2, and E3 ligase activity of Hdm2. These results provide a mechanistic basis for GR and p53 acting as opposing forces in the decision between cell death and survival.

Keywords: Endothelial cells, hypoxia, Bax, p21, PEPCK, G6Pase
Abstract

The development of most tumors is associated with loss of function of the tumor suppressor p53. Different physiological stress, including DNA damage and hypoxia, activate p53. p53 is a transcription factor that regulates genes involved in growth arrest and apoptosis. p53 is down-regulated by its target gene product Mdm2 (human homolog Hdm2). Mdm2 forms an autoregulatory loop with p53 by binding to its N-terminal domain, inhibiting its transcriptional activity and increasing its degradation by the ubiquitin proteasome pathway (for reviews, see Jimenez et al. 1999; Lakin and Jackson 1999; Sionov and Haupt 1999). Mdm2 is a RING finger-dependent ubiquitin protein ligase for p53 and itself (Argentini et al. 2000; Fang et al. 2000; Honda and Yasuda 2000). Mdm2 also inhibits p53 by nuclear export through a mechanism involving either the nuclear export signal (NES) of Mdm2 (Tao and Levine 1999) or the RING finger of Mdm2 and the NES of p53 (Boyd et al. 2000; Geyer et al. 2000). The NES of p53 is masked in the transcriptionally active heterodimer, but is exposed in the monomeric form of p53 (Stommel et al. 1999). MdmX, a Mdm2 homolog that lacks a NES, stabilizes p53 by retention in the nucleus (Jackson and Berberich 2000; Stad et al. 2000). Nuclear p53 levels can also be maintained by ARF, which blocks nucleo-cytoplasmic shuttling of Mdm2 (Sherr and Weber 2000). Most studies of p53 involve DNA damaging drugs and radiation. Much less is known about the physiological stress, hypoxia. Under hypoxic conditions, p53 is stabilized by mitochondria through a redox-dependent mechanism (Chandel et al. 2000) and by HIF-1α (An et al. 1998), whereas p53 induces degradation of HIF-1α (Ravi et al. 2000). The response to hypoxia in vivo also involves the glucocorticoid receptor (GR) (Bauer et al. 1999).

GR is a member of the steroid receptor superfamily that mediates physiological processes controlled by glucocorticoids. In the unbound state GR is located in the cytoplasm bound to chaperones. Upon ligand binding the chaperones dissociate, exposing the NLS that enables GR to enter the nucleus and regulate transcription (Cheung and Smith 2000). GR activates transcription by binding to glucocorticoid response elements (GREs), and represses by binding to negative and composite elements (Kellendonk et al. 1999). GR mediates stress responses, and animals that overexpress GR are more resistant to stress and endotoxic shock (Reichardt et al. 2000).

Recently, evidence has been growing for cross talk between the p53 and GR-mediated responses to stress. p53 physically interacts with and represses the activities of GR (Sengupta et al. 2000b). Modulation of glucocorticoid-induced apoptosis has been linked to p53 gene dosage in mice (Mori et al. 1999). Glucocorticoids prevent p53-induced apoptosis in immortalized human granulosa cells (Sasson et al. 2001). p53 and GR regulate in opposite manners the type II hexokinase gene, whose overexpression is associated with increased glucose catabolism in cancer cells (Mathupala et al. 1997). Hypoxia leads to p53 activation and decreased glucose metabolism (Riva et al. 1998). Because little is known about the functional interactions between the signalling pathways mediated by p53 and GR under physiological conditions, we have investigated how p53 and GR regulate each other under hypoxia. We show that they mutually inhibit each other's activity by cytoplasmic sequestration in a ligand-dependent manner, which leads to increased degradation through recruitment of the E3 ubiquitin ligase Hdm2 and the proteasome pathway.

Acknowledgments

We thank Julia Young for critical reading of the manuscript; D. Bohmann, E. Conseiller, M.R. el-Maghrabi, T. Kietzmann, and J. Shay for the gifts of recombinants; N. Tsuchida for HSC-2 cells; D. Granner, G. de Murcia, and L. Tora for the gift of antibodies; the IGBMC core facilities for help and support; and BioAvenir (Aventis, Rhone-Poulenc), the Centre National de la Recherche Scientifique, the Institut National de la Santé et de la Recherche Médicale, the Hôpital Universitaire de Strasbourg, the Association pour la Recherche sur le Cancer, the Fondation pour la Recherche Médicale, the Ligue Nationale Française contre le Cancer (Equipe labellisée), the Ligue Régionale (Haut-Rhin) contre le Cancer, and the Ligue Régionale (Bas-Rhin) contre le Cancer for financial assistance.

The publication costs of this article were defrayed in part by payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 USC section 1734 solely to indicate this fact.

Acknowledgments

Footnotes

E-MAIL rf.gbsarts-u.cmbgi@hob; FAX 33-3-88-65-32-01.

Article and publication are at http://www.genesdev.org/cgi/doi/10.1101/gad.202201.

Footnotes
Collaboration tool especially designed for Life Science professionals.Drag-and-drop any entity to your messages.